Charging Circuit and Mobile Terminal

ABSTRACT

It is provided a charging circuit and a mobile terminal. The charging circuit is configured to electrically couple a charging interface and a battery of a terminal, and includes a first circuit, a magnetic coupling element, and a second circuit connected in series. The mobile terminal supports a normal charging mode and a fast charging mode.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/371,451, filed on Dec. 7, 2016, which is a continuation ofInternational Application No. PCT/CN2015/080490, filed on Jun. 1, 2015,the entire disclosures of both of which are herein incorporated byreference.

TECHNICAL FIELD

The present disclosure relates to mobile terminal field, andparticularly to a charging circuit and a mobile terminal.

BACKGROUND

With the growing popularity of mobile terminal use, terminal charginghas become a focused issue of mobile terminal providers.

SUMMARY

Disclosed herein are implementations of a charging circuit, configuredto electrically couple a charging interface and a battery, comprising afirst circuit, a magnetic coupling element, and a second circuitconnected in series, wherein the first circuit is configured to receivea first current from the charging interface and convert the firstcurrent to a second current with at least one of a changed magnitude anda changed direction, the magnetic coupling element comprises a firstcoil and a second coil, the first coil connecting with the firstcircuit, the second coil connecting with the second circuit, the firstcoil and the second coil separated from each other to disconnect adirect-current (DC) path of the charging circuit, the magnetic couplingelement is configured to transfer energy from the first coil to thesecond coil in an electromagnetic induction manner by utilizing thesecond current with the at least one of the changed magnitude and thechanged direction to generate a third current, and the second circuit isconfigured to adjust the third current to a fourth current suitable forbattery charging to charge the battery.

Disclosed herein are also implementations of a mobile terminal,comprising a charging interface, a battery, and a charging circuitarranged between the charging interface and the battery, wherein thecharging circuit comprises a first circuit, a magnetic coupling element,and a second circuit connected in series successively between thecharging interface and the battery, the first circuit is configured toreceive a first current from the charging interface and convert thefirst current to a second current with at least one of a changedmagnitude and a changed direction, the magnetic coupling elementcomprises a first coil and a second coil, the first coil connecting withthe first circuit, the second coil connecting with the second circuit,the first coil and the second coil separated from each other todisconnect a direct-current (DC) path of the charging circuit, themagnetic coupling element is configured to transfer energy from thefirst coil to the second coil in an electromagnetic induction manner byutilizing the second current with the at least one of the changedmagnitude and the changed direction to generate a third current, and thesecond circuit is configured to adjust the third current to a fourthcurrent suitable for battery charging to charge the battery.

Disclosed herein are also implementations of a charging circuit,comprising a first circuit, a magnetic coupling element, and a secondcircuit connected in series, the magnetic coupling element comprising afirst coil and a second coil, the first coil connecting with the firstcircuit, the second coil connecting with the second circuit, the firstcoil and the second coil being separated from each other to disconnect adirect-current (DC) path of the charging circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to illustrate the technical solutions of the present disclosureor the related art more clearly, a brief description of the accompanyingdrawings used herein is given below. Obviously, the drawings listedbelow are only examples, and a person skilled in the art should be notedthat, other drawings can also be obtained on the basis of theseexemplary drawings without creative work.

FIG. 1 is a circuit diagram illustrating a charging circuit.

FIG. 2 is a block schematic diagram illustrating a charging circuitaccording to an implementation of the present disclosure.

FIG. 3 is a circuit diagram illustrating a charging circuit according toan example of the present disclosure.

FIG. 4 is a circuit diagram illustrating a charging circuit according toan example of the present disclosure.

FIG. 5 is a circuit diagram illustrating a charging circuit according toan example of the present disclosure.

FIG. 6 is a block schematic diagram illustrating a mobile terminalaccording to an implementation of the present disclosure.

DETAILED DESCRIPTION

FIG. 1 is a circuit diagram illustrating a charging circuit used in amobile terminal. This charging circuit is known as BUCK circuit, whichincludes a MOS transistor, a control circuit, a diode, an inductor, anda battery. Upon charging, the control circuit controls the MOStransistor to turn-on/turn-off to generate a changing square wavecurrent. The square wave current flows to the inductor from the MOStransistor, and then flows to the battery after voltage stabilizationconducted by the inductor.

The above mentioned charging process has a risk of MOS transistorbreakdown. Upon MOS transistor breakdown, the current will flow throughthe inductor, a current/voltage detecting circuit, and the batterydirectly; this will cause the battery to exceed a limit voltage and mayeven lead to more serious consequences.

The cause of the damage to the MOS transistor can be as follows.

The MOS transistor is mis-energized; the voltage at both ends of the MOStransistor exceeds a maximum voltage that can be withstood;electrostatic breakdown or surge.

The MOS transistor is of poor quality; or, there is an integratedmanufacture technology issue.

There can be other defects.

In order to avoid the above problems and improve the reliability of theMOS transistor, the value of on-resistance (RDSON) of the MOS transistorhas been increased so as to improve the voltage resistance of the MOStransistor. On the other hand, high resistance, in turn, would cause thecharging circuit to be easy to heat, low energy transmission efficiencyand so on.

Technical solutions of the implementations of the present disclosurewill be described clearly and completely taken in conjunction with theaccompanying drawings; it will be apparent to one of ordinary skill inthe art that, the implementations described below are merely a part ofthe disclosure and other implementations obtained out of them withoutcreative work will fall into the protection range of the presentdisclosure either.

Implementation 1

According to implementation 1 of the present disclosure, it provides acharging circuit. In the following, the components of the chargingcircuit will be described in detail. A person skilled in the art will beable to arrange or assemble the charging circuit in accordance teachingof the description by using routine methods of experimentation oranalysis without undue efforts. Any method used to assemble the chargingcircuit of the present disclosure will fall into the protection scopedefined by the appending claims.

FIG. 2 is block schematic diagram illustrating the charging circuit. Asshown in FIG. 2, a charging circuit 30 is arranged between a charginginterface 10 and a battery 20 of a terminal for electrically couplingthe charging interface 10 and the battery 20. The charging circuit 30includes a first circuit 31, a magnetic coupling element 33, and asecond circuit 32 connected in series successively between the charginginterface 10 and the battery 20. The magnetic coupling element 33includes a first coil 331 and a second coil 332. The first coil 331connects with the first circuit 31, and the second coil 332 connectswith the second circuit 32, the first coil 331 and the second coil 332separated apart from each other so as to disconnect a direct-current(DC) path of the charging circuit 30.

Configurations and operations of the components of the charging circuitwill be described in detail below.

The first circuit 31 is configured to receive a first current from thecharging interface 10 and convert the first current to a second currentwith changed magnitude and/or direction.

The magnetic coupling element 33 is configured to transfer energy fromthe first coil 331 to the second coil 332 in an electromagneticinduction manner by utilizing the second current with changed magnitudeand/or direction, so as to generate a third current (in other words, thethird current is generated at the second coil 332 and is output to thesecond circuit 32).

The second circuit 32 is configured to adjust alternating current (AC),which is coupled to the second circuit 32 by the first circuit 31through the magnetic coupling element 33, to DC which is suitable forbattery charging.

In this technical scheme, a DC path of the charging circuit is separatedby the magnetic coupling element. That is to say, there is no DC path inthe charging circuit. DC current from the charging interface would notbe output directly to the second circuit and the battery upon failure ofthe first circuit, whereby reliability of the charging circuit isimproved.

Example 1

FIG. 3 is a circuit diagram illustrating a charging circuit according toExample 1. As shown in FIG. 3, the first circuit 31 includes ahalf-bridge circuit 312 and a control circuit 311 controlling thehalf-bridge circuit. With the aid of the half-bridge circuit 312,efficiency of the whole circuit can be improved.

The half-bridge circuit 312 includes a first switch transistor T1 and asecond switch transistor T2. A first end of the first switch transistorT1 connects with the charging interface 10, a second end of the firstswitch transistor T1 connects with a first end of the first coil 331,and a control end of the first switch transistor T1 connects with thecontrol circuit 311. A first end of the second switch transistor T2connects with the second end of the first switch transistor T1, a secondend of the second switch transistor T2 connects to ground, and a controlend of the second switch transistor T2 connects to the control circuit311. A second end of the first coil 331 connects to ground. Furthermore,two ends of the second coil 332 can connect with the second circuit 32and ground respectively. Besides, the second circuit 32 can be grounded.

Typically, a switch transistor (such as a MOS transistor), which is easybreakdown, is arranged within the first circuit. When breakdown of theswitch transistor occurs, the first circuit could not convert DC to ACvia the switch transistor; this cause DC input at the charging interfacebeing applied to a subsequent component of the charging interface or abattery directly. However, in this example, with the aid of the magneticcoupling element arranged between the first circuit and the secondcircuit, a DC path of the charging circuit can be disconnected. That isto say, DC input at the charging interface cannot flow to the secondcircuit or the battery even if the switch transistor in the firstcircuit is broke down or failure, whereby the reliability of thecharging circuit of the mobile terminal can be improved.

In addition, the magnetic coupling element has good isolationperformance. Thus, instead of increasing the on-resistance so as toincrease the voltage resistance of the MOS transistor and then improvethe reliability of the circuit like in the prior art, in implementationsof the present disclosure, a lower on-resistance of the switchtransistor in the first circuit is allowed, and this will improve theenergy transfer efficiency of the whole charging circuit while reducingheating and loss.

Example 2

FIG. 4 is a circuit diagram illustrating a charging circuit according toExample 2. As shown in FIG. 4, the first circuit 31 includes afull-bridge circuit 313 and a control circuit 311 controlling thefull-bridge circuit. A difference between example 1 and example 2 isthat, in example 2, the full-bridge circuit 313 is used to replace thehalf-bridge circuit 312 in example 1. With the aid of the full-bridgecircuit 313, efficiency of the whole circuit can be further improved.

The full-bridge circuit 313 includes a first switch transistor T1, asecond switch transistor T2, a third switch transistor T3, and a fourthswitch transistor T4. A first end of the first switch transistor T1connects with the charging interface 10, a second end of the firstswitch transistor T1 connects with a second end of the first coil 331,and a control end of the first switch transistor T1 connects with thecontrol circuit 311. A first end of the second switch transistor T2connects with the second end of the first switch transistor T1, a secondend of the second switch transistor T2 connects to ground, and a controlend of the second switch transistor T2 connects with the control circuit311. A first end of the third switch transistor T3 connects with thecharging interface 10, a second end of the third switch transistor T3connects with the first end of the first coil 331, and a control end ofthe third switch transistor T3 connects with the control circuit 311. Afirst end of the fourth switch transistor T4 connects with the secondend of the third switch transistor T3, a second end of the fourth switchtransistor T4 connects to ground, and a control end of the fourth switchtransistor T4 connects with the control circuit 311. In addition, twoends of the second coil 332 can connect with the second circuit 32, andthe second circuit can be grounded.

A switch transistor (such as a MOS transistor), which is easy breakdown,is arranged within the first circuit. When breakdown of the switchtransistor occurs, the first circuit could not convert DC to AC via theswitch transistor; this cause DC input at the charging interface beingapplied to a subsequent component of the charging interface or a batterydirectly. However, in this example, with the aid of the magneticcoupling element arranged between the first circuit and the secondcircuit, a DC path of the charging circuit can be disconnected. That isto say, DC input at the charging interface cannot flow to the secondcircuit or the battery even if the switch transistor in the firstcircuit is broke down or failure, whereby the reliability of thecharging circuit of the mobile terminal can be improved.

In addition, the magnetic coupling element has good isolationperformance. Thus, instead of increasing the on-resistance so as toincrease the voltage resistance of the MOS transistor and then improvethe reliability of the circuit like in the prior art, in implementationsof the present disclosure, a lower on-resistance of the switchtransistor in the first circuit is allowed, and this will improve theenergy transfer efficiency of the whole charging circuit while reducingheating and loss.

Example 3

FIG. 5 is a circuit diagram illustrating a charging circuit according toExample 3. As shown in FIG. 5, the first circuit 31 includes a switchtransistor 317 and a control circuit 311 controlling the switchtransistor. A difference between example 3 and example 1-2 is that, inexample 3, a switch transistor is used to replace the half-bridgecircuit/full bridge circuit, whereby the cost of the circuit can bereduced.

A first end of the switch transistor 317 connects with the charginginterface 10, a second end of the switch transistor 317 connects with afirst end of the first coil 331, and a control end of the switchtransistor 317 connects with the control circuit 311. A second end ofthe first coil 331 connects to ground.

In short, as can be seen from the above description, technical schemesof the implementations of the present disclosure can improve thereliability of the charging circuit through a minor modification to therelated art.

The switch transistor in the first circuit referred to herein includesmultiple metal oxide semiconductor field effect transistors (MOSFET).

As an implementation, the second circuit 32 referred to herein caninclude a rectifier circuit 321 and a filter circuit 322.

Implementation 2

According to Implementation 2 of the present disclosure, it is provideda mobile terminal. FIG. 6 is a block schematic diagram illustrating themobile terminal. As shown in FIG. 6, a mobile terminal 60 includes acharging interface 61, a battery 62, and a charging circuit 63. Thecharging circuit 63 can adopt any of the implementations of the chargingcircuit 30 described above.

For details of the charging circuit 63, please refer to the chargingcircuit 30 described above with refer to FIG. 2-FIG. 5, and it will notbe described here again in order to avoid redundancy.

In the technical scheme described above, a DC path of the chargingcircuit is separated by the magnetic coupling element. That is to say,there is no DC path in the charging circuit. DC current from thecharging interface would not be output directly to the second circuitand the battery upon failure of the first circuit, whereby reliabilityof the charging circuit is improved.

As an implementation, the charging interface 51 is a universal serialbus (USB) interface or any other interface corresponds to relatedindustry standards of terminal charging interface.

As an implementation, the battery 20 is lithium battery.

As an implementation, the mobile terminal 50 supports a normal chargingmode and a fast charging mode, wherein charging current is larger in thefast charging mode than in the normal charging mode.

It should be understood that the phenomenon of MOS transistor breakdownis particularly serious in the mobile terminal which supports fastcharging. As to the problem of circuit unreliability upon fast chargingcaused by MOS transistor breakdown, the mobile terminal according to theimplementation of the present disclosure can be a good solution.

A person skilled in the art will understand, exemplary units oralgorithm steps described in any of the implementations can be achievedvia electronic hardware or a combination of electronic hardware andcomputer software. Whether hardware or software should be adopteddepends on design constraints and specific applications of the technicalschemes. Respective specific application can use different methods ormanners to achieve the function described in the implementations, whichwill fall into the protection scope of the present disclosure.

Specific operations of the device, system, and the unit or module cancross-refer to corresponding descriptions according to theimplementation, and will not go into much detail here.

In the implementations of the present disclosure, the device and systemdescribed herein can be achieved in other manners. The configuration ofthe device according to the implementation described above is onlyexemplary; the division of units in the device is a kind of divisionaccording to logical function, therefore there can be other divisions inpractice. For example, multiple units or components can be combined orintegrated into another system; or, some features can be ignored whilesome units need not to be executed. On the other hand, various functionunits can be integrated into one processing unit; two or more than twounits can be integrated into one unit; or, each unit is physicallyseparate.

Furthermore, various function units can be integrated into oneprocessing unit; two or more than two units can be integrated into oneunit; or, each unit is physically separate.

Operations or functions of technical schemes according to theimplementations of the present disclosure, when achieved in the form ofsoftware functional units and sold or used as an independent product,can be stored in a computer readable storage medium. According to this,all or a part of the technical schemes of the present disclosure can berealized in the form of software products which can be stored in astorage medium. The storage medium includes USB disk, Read Only Memory(ROM), Random Access Memory (RAM), magnetic disk, CD, and any othermedium that can be configured to store computer-readable program code orinstructions. The computer-readable program code, when executed on adata-processing apparatus (can be personal computer, server, or networkequipment), adapted to perform all or a part of the methods described inthe above-mentioned implementations.

The foregoing descriptions are merely preferred implementations of thepresent disclosure, rather than limiting the present disclosure. Variousmodifications and alterations may be made to the present disclosure forthose skilled in the art. Any modification, equivalent substitution,improvement or the like made within the spirit and principle of thepresent disclosure shall fall into the protection scope of the presentdisclosure.

What is claimed is:
 1. A charging circuit, configured to electricallycouple a charging interface of a mobile terminal and a battery of themobile terminal, the charging circuit comprising a first circuit, amagnetic coupling element, and a second circuit connected in series,wherein the mobile terminal supports a normal charging mode and a fastcharging mode, and charging current is larger in the fast charging modethan in the normal charging mode; the first circuit is configured toreceive a first current from the charging interface and convert thefirst current to a second current with at least one of a changedmagnitude and a changed direction; the magnetic coupling elementcomprises a first coil and a second coil, the first coil connecting withthe first circuit, the second coil connecting with the second circuit,the first coil and the second coil separated from each other todisconnect a direct-current (DC) path of the charging circuit; themagnetic coupling element is configured to transfer energy from thefirst coil to the second coil in an electromagnetic induction manner byutilizing the second current with the at least one of the changedmagnitude and the changed direction to generate a third current; and thesecond circuit is configured to adjust the third current to a fourthcurrent suitable for battery charging to charge the battery.
 2. Thecharging circuit of claim 1, wherein the first circuit comprises ahalf-bridge circuit and a control circuit controlling the half-bridgecircuit, and the half-bridge circuit comprises a first switch transistorand a second switch transistor, wherein the first switch transistor hasa first end configured to connect with the charging interface, a secondend connected with a first end of the first coil, and a control endconnected with the control circuit; the second switch transistor has afirst end connected with the second end of the first switch transistor,a second end configured to connect to ground, and a control endconnected with the control circuit; and the first coil has a second endconfigured to connect to ground.
 3. The charging circuit of claim 1,wherein the first circuit comprises a full-bridge circuit and a controlcircuit controlling the full-bridge circuit, and the full-bridge circuitcomprises a first switch transistor, a second switch transistor, a thirdswitch transistor, and a fourth switch transistor, wherein the firstswitch transistor has a first end configured to connect with thecharging interface, a second end connected with a second end of thefirst coil, and a control end connected with the control circuit; thesecond switch transistor has a first end connected with the second endof the first switch transistor, a second end configured to connect toground, and a control end connected with the control circuit; the thirdswitch transistor has a first end configured to connect with thecharging interface, a second end connected with a first end of the firstcoil, and a control end connected with the control circuit; and thefourth switch transistor has a first end connected with the second endof the third switch transistor, a second end configured to connect toground, and a control end connected with the control circuit.
 4. Thecharging circuit of claim 1, wherein the first circuit comprises aswitch transistor and a control circuit controlling the switchtransistor; the switch transistor has a first end configured to connectwith the charging interface, a second end connected with a first end ofthe first coil, and a control end connected with the control circuit;and the first coil has a second end configured to connect to ground. 5.The charging circuit of claim 4, wherein the switch transistor in thefirst circuit is metal oxide semiconductor field effect transistor(MOSFET).
 6. The charging circuit of claim 1, wherein the second circuitcomprises a rectifier circuit and a filter circuit.
 7. The chargingcircuit of claim 1, wherein the first circuit comprises at least onetransistor having an on-resistance, wherein the on-resistance has afirst value when a voltage resistance of the at least one transistor isincreased, wherein the on-resistance has a second value when the voltageresistance of the at least one transistor is not increased, wherein thesecond value is less than the first value.
 8. A mobile terminalcomprising a charging interface, a battery, and a charging circuitarranged between the charging interface and the battery, wherein themobile terminal supports a normal charging mode and a fast chargingmode, and charging current is larger in the fast charging mode than inthe normal charging mode; the charging circuit comprises a firstcircuit, a magnetic coupling element, and a second circuit connected inseries successively between the charging interface and the battery; thefirst circuit is configured to receive a first current from the charginginterface and convert the first current to a second current with atleast one of a changed magnitude and a changed direction; the magneticcoupling element comprises a first coil and a second coil, the firstcoil connecting with the first circuit, the second coil connecting withthe second circuit, the first coil and the second coil separated fromeach other to disconnect a direct-current (DC) path of the chargingcircuit; the magnetic coupling element is configured to transfer energyfrom the first coil to the second coil in an electromagnetic inductionmanner by utilizing the second current with the at least one of thechanged magnitude and the changed direction to generate a third current;and the second circuit is configured to adjust the third current to afourth current suitable for battery charging to charge the battery. 9.The mobile terminal of claim 8, wherein the first circuit comprises ahalf-bridge circuit and a control circuit controlling the half-bridgecircuit, and the half-bridge circuit comprises a first switch transistorand a second switch transistor, wherein the first switch transistor hasa first end connected with the charging interface, a second endconnected with a first end of the first coil, and a control endconnected with the control circuit; the second switch transistor has afirst end connected with the second end of the first switch transistor,a second end configured to connect to ground, and a control endconnected with the control circuit; and the first coil has a second endconfigured to connect to ground.
 10. The mobile terminal of claim 8,wherein the first circuit comprises a full-bridge circuit and a controlcircuit controlling the full-bridge circuit, and the full-bridge circuitcomprises a first switch transistor, a second switch transistor, a thirdswitch transistor, and a fourth switch transistor, wherein the firstswitch transistor has a first end connected with the charging interface,a second end connected with a second end of the first coil, and acontrol end connected with the control circuit; the second switchtransistor has a first end connected with the second end of the firstswitch transistor, a second end configured to connect to ground, and acontrol end connected with the control circuit; the third switchtransistor has a first end connected with the charging interface, asecond end connected with a first end of the first coil, and a controlend connected with the control circuit; and the fourth switch transistorhas a first end connected with the second end of the third switchtransistor, a second end configured to connect to ground, and a controlend connected with the control circuit.
 11. The mobile terminal of claim8, wherein the first circuit comprises a switch transistor and a controlcircuit controlling the switch transistor; the switch transistor has afirst end connected with the charging interface, a second end connectedwith a first end of the first coil, and a control end connected with thecontrol circuit; and the first coil has a second end configured toconnect to ground.
 12. The mobile terminal of claim 8, wherein thecharging interface is a universal serial bus (USB) interface.
 13. Themobile terminal of claim 8, wherein the battery is a lithium battery.14. The mobile terminal of claim 8, wherein the first circuit comprisesat least one transistor having an on-resistance, wherein theon-resistance has a first value when a voltage resistance of the atleast one transistor is increased, wherein the on-resistance has asecond value when the voltage resistance of the at least one transistoris not increased, wherein the second value is less than the first value.15. A charging circuit comprising a first circuit, a magnetic couplingelement, and a second circuit connected in series between a charginginterface of a mobile terminal and a battery of the mobile terminal, themagnetic coupling element comprising a first coil and a second coil, thefirst coil connecting with the first circuit, the second coil connectingwith the second circuit, the first coil and the second coil beingseparated from each other to disconnect a direct-current (DC) path ofthe charging circuit, wherein the mobile terminal supports a normalcharging mode and a fast charging mode, and charging current is largerin the fast charging mode than in the normal charging mode.
 16. Thecharging circuit of claim 15, wherein the first circuit comprises ahalf-bridge circuit and a control circuit controlling the half-bridgecircuit, and the half-bridge circuit comprises a first switch transistorand a second switch transistor, wherein the first switch transistor hasa first end configured to connect with the charging interface, a secondend connected with a first end of the first coil, and a control endconnected with the control circuit; the second switch transistor has afirst end connected with the second end of the first switch transistor,a second end configured to connect to ground, and a control endconnected with the control circuit; and the first coil has a second endconfigured to connect to ground.
 17. The charging circuit of claim 15,wherein the first circuit comprises a full-bridge circuit and a controlcircuit controlling the full-bridge circuit, and the full-bridge circuitcomprises a first switch transistor, a second switch transistor, a thirdswitch transistor, and a fourth switch transistor, wherein the firstswitch transistor has a first end configured to connect with thecharging interface, a second end connected with a second end of thefirst coil, and a control end connected with the control circuit; thesecond switch transistor has a first end connected with the second endof the first switch transistor, a second end configured to connect toground, and a control end connected with the control circuit; the thirdswitch transistor has a first end configured to connect with thecharging interface, a second end connected with a first end of the firstcoil, and a control end connected with the control circuit; and thefourth switch transistor has a first end connected with the second endof the third switch transistor, a second end configured to connect toground, and a control end connected with the control circuit.
 18. Thecharging circuit of claim 15, wherein the first circuit comprises aswitch transistor and a control circuit controlling the switchtransistor; the switch transistor has a first end configured to connectwith the charging interface, a second end connected with a first end ofthe first coil, and a control end connected with the control circuit;and the first coil has a second end configured to connect to ground. 19.The charging circuit of claim 18, wherein the switch transistor in thefirst circuit is metal oxide semiconductor field effect transistor(MOSFET).
 20. The charging circuit of claim 15, wherein the firstcircuit comprises at least one transistor having an on-resistance,wherein the on-resistance has a first value when a voltage resistance ofthe at least one transistor is increased, wherein the on-resistance hasa second value when the voltage resistance of the at least onetransistor is not increased, wherein the second value is less than thefirst value.